|Publication number||US7025831 B1|
|Application number||US 09/443,663|
|Publication date||Apr 11, 2006|
|Filing date||Nov 19, 1999|
|Priority date||Dec 21, 1995|
|Publication number||09443663, 443663, US 7025831 B1, US 7025831B1, US-B1-7025831, US7025831 B1, US7025831B1|
|Inventors||Jeffery W. Butterbaugh, David C. Gray, Robert T. Fayfield, Kevin Siefering, John Heitzinger, Fred C. Hiatt|
|Original Assignee||Fsi International, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (65), Non-Patent Citations (14), Referenced by (31), Classifications (23), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation of application Ser. No. 08/860,071, filed Sep. 02, 1997 now U.S. Pat. No. 6,015,503, which is a Continuation of US national stage entry of PCT/US95/16649, filed 21 Dec. 1995.
1. Field of the Invention
The present invention relates to an apparatus which provides for the conditioning of the surface of a substrate in a plasma-less gas phase environment. It finds particular application in etching, cleaning, or bulk stripping removal of films or contaminants from the surface of a semiconductor wafer for use in the fabrication of integrated circuits.
2. Description of the Related Art
The traditional standard for surface contamination removal in the semiconductor industry is the RCA clean which uses liquid aqueous chemicals. Highly selective bulk film stripping is also commonly carried out with liquid aqueous chemicals. The liquid aqueous chemical processes have problems involving safety, waste disposal, cleanliness and cost, and these problems make the use of gaseous processes very attractive.
The use of plasma containing reactive gas mixtures or reactive ion etching (RIE) are an alternative to liquid aqueous chemical processes. In these type of processes, the container is filled with a low pressure gas, the substrate is inserted into the container along with a reactive etchant gas. Voltage is applied to excite the gas, which chemically reacts with the surface. These types of processes have the disadvantage of causing additional damage and contamination of the substrate surface. It is also known to use the effluent of a gas plasma having at least one reactive specie, but being substantially free of electrically charged particles. This is known in the art as a downstream plasma source and is shown in U.S. Pat. No. 4,687,544 to Bersin, entitled “Method And Apparatus For Dry Processing of Substrates”.
Plasma-less UV treatments have also been disclosed before. For example, U.S. Pat. No. 2,841,477 to Hall, entitled “Photochemically Activated Gaseous Etching Method” is the earliest known reference teaching a process of using a photochemically activated gas to etch semiconductor materials. This reference shows an etching method involving the steps of immersing the semiconductor material in a photolyzable gas and directing UV light toward the portion of the material to be etched. The gas is apparently static. The UV light causes the photolyzable gas to dissociate into various chemically active species which react with the substrate surface.
U.S. Pat. No. 3,122,463 to Ligenza, entitled “Etching Technique for Fabricating Semiconductor Or Ceramic Devices” is another example showing a method of using photochemically activated F2O gas to etch semiconductor materials. This reference shows a method of immersing the semiconductor material in a static gas and directing UV light toward the portion of the material to be etched.
Processes of the type disclosed in Hall or Ligenza have the disadvantages of non-uniform gas distribution and of a static gas regime which does not allow the transport of contaminants and etching residues out of the reactor during the etch reaction.
It has been known to use a flow of gas across the surface of a substrate in an etching process. Such processes provide excellent process control and reduce accumulation of contamination and residue at the wafer surface. For example, U.S. Pat. No. 4,749,440 to Blackwood et al, entitled “Gaseous Process And Apparatus For Removing Films From Substrates” assigned to FSI Corporation and Texas Instruments Inc. shows a device which causes anhydrous reactive gas to flow over the substrate in the presence of water vapor, to chemically react with the surface.
U.S. Pat. No. 5,022,961 to Izumi et al, entitled “Method For Removing A film On A Silicon Layer Surface” shows a device, substantially identical to the device of U.S. Pat. No. 4,749,440, which is used to etch silicon oxide using HF and alcohol cases directed across the surface of a substrate wafer.
U.S. Pat. No. 5,228,206 to Grant et al, entitled “Cluster Tool Dry Cleaning System” shows a device which directs a flow of reactive gas across the surface of a substrate and asserts that UV radiation causes the gas to photochemically react with the substrate surface. In the device of this reference the substrate is rotated to obtain more uniform UV flux on the substrate surface.
Examples of plasma-less gaseous processes include, in addition to the UV activated processes of Hall and Ligenza, the non-UV processes disclosed in the Blackwood and Izumi references and the UV-activated processes disclosed in U.S. patent application Ser. No. 08/292,359 filed Aug. 18, 1994 and in U.S. patent application Ser. No. 08/259,542 filed Jun. 14, 1994.
Applicants have found that systems of the type directing a flow of gas which chemically reacts, with or without photochemical activation, with the substrate as it flows across the surface provides undesirable non-uniform etching, cleaning or bulk stripping. Typically, more etching takes place on the side of the substrate where the flow starts, and less reaction occurs as the gas flows across the surface due to depletion of reactant gas. Applicants have also found that a device employing rotation of the substrate, in combination with the flow of gas across the substrate can cause a vortex or eddy effect which also can produce undesirable non-uniform effects.
All of the methods or devices discussed above have the disadvantage of either non-uniform gas distribution or non-uniform UV illumination, and the further disadvantage that none of the prior processes remove gas which has reacted with the substrate in a manner which minimizes the risk of further contamination.
In JP 57-200569 (1982) there is disclosed an apparatus for treating a wafer with a UV activated gas, the gas being activated while in a first high pressure region. The gas is passed through a single slit to a lower pressure region where it contacts a wafer carried on a belt moving under the slit.
U.S. Pat. No. 4,540,466 entitled “Method Of Fabricating Semiconductor Device By Dry Process Utilizing Photochemical Reaction, and Apparatus Therefor” to Nishizawa and assigned to Semiconductor Research Foundation, shows a device with a higher pressure gas region and a lower pressure gas region, which causes the reactive gas to flow toward the substrate surface, as opposed to directing the flow across the surface as discussed above in connection with Izumi, Blackwood or Grant. The mean free path of the gaseous particles in the high pressure region is shorter than the openings between the two regions, i.e. a viscous flow regime. The pressure in the lower pressure region is set to provide a mean free path of the gaseous particles which is greater than the diameter of the chamber, i.e. a molecular flow regime. Nishizawa does not consider the hydrodynamics at the substrate surface, but the molecular flow regime in the lower pressure region precludes a radial laminar flow of gas across the substrate surface.
The purpose of the present invention is to provide an apparatus for conditioning of the surface of a substrate, in a preferably plasma-less gas phase environment, which overcomes the limitations of the prior art described above. The invention overcomes the limitations discussed above by creating a uniform peripherally directed gas flow which causes the gas, after it has reacted with the substrate surface, to flow radially outward to the substrate edge. The invention also overcomes the limitations discussed above by operating in a viscous flow regime. The present invention can be used to perform all of the plasma-less methods discussed above in connection with the prior art, and to obtain better results.
The present invention overcomes the problems described above by providing an apparatus and process for conditioning a substrate, such as a silicon wafer, contained in an isolatable chamber fed with a conditioning gas including a reactive gas. The apparatus comprises a chamber isolatable from the ambient environment and including a first gas inlet portion into which the conditioning gas is fed and a conditioning portion in which the substrate is conditioned with said conditioning gas; support means for supporting the substrate in the conditioning portion of the chamber; first pressure bias means for establishing a first pressure bias in the chamber such that the conditioning gas in the gas inlet portion of the chamber is established at a first pressure and the conditioning gas in the conditioning portion is provided to the substrate at a second lower pressure than the first pressure, both said first and second pressures being provided in a viscous flow regime; inlet means for feeding conditioning gas into the gas inlet portion of the chamber so that the pressure differential between the gas inlet and conditioning portions of the chambers causes the conditioning gas to flow toward the first surface of the substrate wherein the reactive gas component thereof will chemically react with and condition the first substrate surface; second pressure bias means for creating a second pressure bias across the first surface of the substrate such that the conditioning gas, after it has chemically reacted with the substrate surface, flows outward from where it has reacted, off of the substrate toward the periphery of the chamber; and exhaust means for exhausting gas from the chamber.
The apparatus may further include a light generator provided externally of the chamber to direct light of a wavelength range effective to activate a photochemical reaction of the conditioning gas or the substrate or both at the substrate surface.
Embodiments for one side conditioning or two side conditioning of the substrate are disclosed. Variations to accomplish these results include one side feed and two side feed of conditioning gas and of one side or dual side irradiation of the substrate.
A detailed description of the invention is hereafter described with specific reference being made to the drawings in which:
While this invention may be embodied in many different forms, there are shown in the drawings and described in detail herein specific preferred embodiments of the invention. The present disclosure exemplifies the principles of the invention. This disclosure is not intended to limit the invention to the particular embodiments illustrated.
The conditioning gas can be any type of gas known for use in etching, cleaning, bulk stripping or otherwise conditioning the surface of a substrate, but in the preferred embodiment the gas will be comprised of an inert gas such as nitrogen mixed with a reactive gas. The reactive gas may be any type of well known reactive gas, for example HF, HF/water vapor, HF/alcohol vapor, a photolyzable fluorine containing gas such as ClF3, F2 or a ClF3/Cl2 mixture, or may also be the effluent of a gas plasma from a downstream plasma source, as discussed in Bersin above, having at least one reactive specie, but being substantially free of electrically charged particles (i.e. a plasma-less gas). Mixtures of reactive gases may also be employed. For light cleaning the reactive gas may be as low as 1% of the gas, while in bulk stripping the gas may be 100% reactive gas. If the process to be performed does not require photochemical activation, then plates 36 and 38 could be made of an opaque material. In the processes in which a photoreactive gas is used, it should be understood that other materials could be used, as long as they are inert and transparent to the wavelength of light desired to activate the gas, and, if desired, to heat the substrate. The substrate in the preferred embodiment is most commonly a semiconductor substrate, but it can be any type of substrate upon which surface conditioning is desired. Examples include glass substrates (such as flat panel displays), thin film substrates (such as thin film disk heads), and ceramic substrates.
The reaction region 32 (second region discussed above in connection with
The conditioning gas is supplied through gas manifold 48 to annular channel 50, which opens into the gas inlet region 30. Gas is introduced into the annular channel 50 surrounding the chamber and then flows through the gap between the solid sapphire plate 36 and the perforated sapphire plate 38 and then through the perforations 52 in the perforated sapphire plate into the reaction region 32 between the perforated sapphire plate 38 and the baffle plate 40. The annular channel 50 is designed so that its flow conductance is larger compared to the flow conductance of the gap between the solid sapphire plate 36 and the perforated sapphire plate 38 so that the pressure in the annular channel 50 is approximately equal around the entire circumference even though the reactive gases are introduced to the channel through a single small diameter tube 48. Applicants have found that the flow conductance of the annular channel should be at least 10 times the flow conductance of the gap between the plates to insure that the gas feeds uniformly around the circumference of the annular channel. The isobaric nature of the annular ring 50 provides circumferential uniform flow of the gas from the edge to the center of the perforated plate 38. Further, the size and plurality of the perforations 52 in the perforated sapphire plate 38 are designed so that the flow conductance of the perforations 52 is much less than the flow conductance of the gap between the solid sapphire plate 36 and the perforated sapphire plate 38 so that the flow of gas through each perforation 52 is approximately equal. Top clamp 54 is used to hold solid sapphire plate 36 in place. Channel cover 56, together with chamber wall 34 defines the annular channel gap through which conditioning gas flows into the gas inlet region 30. In the embodiment of
Referring now to
Applicants have experimented with various numbers of perforations, perforation spacing, flow rate, and spacing between the plate 38 and the surface of the semiconductor substrate or wafer.
In the tests the diameter d was 1 mm in a 1.9 mm thick sapphire or aluminum plate. Thermal oxide on silicon wafers was etched at total flows of 500 and 2000 sccm in an HF/IPA oxide etching system, and at spacings (S) of 1 and 6 cm, using a 69-hole, 12.7 mm pitch (g) hole pattern (sapphire plate), a 69-hole, 6.3 mm pitch hole pattern (aluminum plate), and a 221 hole, 12.7 mm pitch hole pattern (aluminum plate). Pressure, temperature and process time were held constant. The reactor pressure was 100 torr, the temperature was 40° C. and the process time was 5 minutes. The etching rate of oxide was determined by measuring the oxide film thickness with a spectroscopic reflectometer before and after the process run. 150 mm diameter wafers and 200 mm diameter wafers were used. The test results are shown in Table 1 below:
A rough calculation of the amount of diffusional mixing from the incoming streams from the perforations was made by assuming the binary diffusion of the reactant from each stream perpendicular to the flow of the stream as illustrated in
where D is the binary diffusivity of the reactant gas in the nitrogen diluent, t is the time for the flow to travel from the perforation to the wafer surface (the perforation to wafer spacing divided by average velocity of gas as it leaves the perforation), and g is the center to center perforation spacing. It can be shown that X goes as the +0.5 power of s and the −0.5 power of the mass flow. The data shows a strong correlation between uniformity and X. It would appear from the data that an X greater than 0.10 prevented a pattern from appearing below the perforations and provided good etching uniformity.
It was also calculated that with the entrance pressure set at 100 torr (measured at the opening of the annular channel into the gas inlet region) that the pressure drop to the center of the perforated plate was insignificant, measuring approximately 0.02–0.16 mTorr, that the greatest pressure drop took place through the perforations 2.9–38 mTorr, and that the pressure drop through the peripheral gap, the outlet gap and to the exhaust outlet was approximately 0.08–0.36 mTorr. Therefore, it can be seen that the pressure drop from the entrance to the exit is small relative to the pressure at the entrance, thereby ensuring a viscous flow regime. The pressure across the perforated plate dominates all other pressure drops. This assures that the pressure drop across the perforated plate will be radially uniform, resulting in a uniform flow of gas through each perforation.
U.S. patent application Ser. No. 08/292,359 filed Aug. 18, 1994 discloses a process for selective etching of silicon nitride using a photolyzable fluorine containing gas such as ClF3/Cl2 mixture. The intensity of UV required to achieve suitable activation above the substrate over the range of 180–400 nm is desirably at least 50 mW/cm2, preferably at least 200 mW/cm2. A typical broad-band UV source useful in the invention will provide an integrated intensity over the 180–400 nm range of about 250 mW/cm2 with a intensity at 254±5 nm of about 25 mW/cm2.
Applicants have found that with a gas inlet pressure of 100 torr that a grid pattern of perforations 52 of between 6 and 13 mm, center to center, with each perforation being approximately 1 mm in diameter allows the reactive gas to uniformly fill the gas inlet region 30 so that approximately equal amounts of gas will flow through each perforation 52 from the higher pressure gas inlet region 30 to the lower pressure reaction region 32.
U.S. patent application Ser. No. 08/259,542 filed Jun. 14, 1994 discloses a cleaning method for removing silicon oxides, as well as metals or other contaminants, from the surface of the substrate such as silicon, gallium, arsenide, or silicon oxide. The process utilizes a conditioning gas which includes at least one photolyzable fluorine containing gas such as ClF3, optionally with a facilitating gas such as chlorine, and/or an inert gas such as dry nitrogen. The substrate is exposed to UV irradiation in the presence of the conditioning gas. Typical conditions use a conditioning gas of 1–90% ClF3, 0–25% Cl2, and the balance nitrogen, at a total gas pressure of about 100 torr and a flow rate of 1000 sccm and broad band UV irradiation from a medium pressure mercury arc lamp. The process can be used to remove silicon oxide, giving very low selectivity between various oxide forms, as well as to remove metallic contamination, from semiconductor substrates. The cleaning method disclosed in Ser. No. 08/259,542 is especially advantageous when practiced using the apparatus and method of the present invention.
Referring now to
Referring now to
Referring now to
Referring now to
Referring now to
Referring now to
While conditioning gas and reaction products are drawn readily off the top of wafer 120 and directly to the perimeter channels 112, 114, and 116, conditioning gas is also accessible to the underside of wafer 20 via diffusion. A solid light transmissive window 122 is provided on the bottom of the chamber. Preferably windows 108 and 122 and showerhead 110 are made of a material transparent to both IR and UV light. Light sources 124, and 126 located respectively above and below chamber 105 whose output is effective to activate photochemical reaction of the conditioning gas or the substrate or both, are provided to allow for optional topside and underside irradiation on both sides of the wafer. Suitably the light sources 124, 126 are UV generators such as a medium pressure mercury lamps, arc or flash lamps or dielectric discharge lamps. The output of the light source 124 or of light source 126 may be directed directly into the chamber 105, or indirectly such as via a dichroic cold mirror 128 which filters IR light so that the UV source 124 does not significantly affect the temperature of the wafer 120. Temperature control is suitably provided by one or more IR lamps on the underside of chamber 105 whose output is directed through window 122 to the bottom side of wafer 120.
It is also possible to use channel 116 to feed reactive or inert gas, as desired, to the underside of the wafer via opening 140 in window 138. In this case central perimeter channels 112 and 114 are used to exhaust the gases fed into the chamber from both channels 106 and 116. However, underside feeding of reactive or inert gas is preferably provided by the chamber 155 shown in
Chamber 155 in
The wafer 120 is held in place within the chamber by support pins 210, 212 and 214, suitably made of quartz or other material which is substantially non-reactive to the conditioning gas environment. Pins 210 and 212 feed through housing 200 and are desirably equipped with thermocouple temperature sensors at the interior wafer contacting ends thereof and electrical connections thereto running through 210 and 212 to the exterior of housing 200, to thereby provide means for monitoring the temperature of the wafer.
Reactive gas is fed into the annular gas inlets 106 and 116 of chamber 155 through feed lines 220 and 222. Exhausts ports 224 and 226 communicate with channels 112 and 114 via valves 225 and 227 respectively, to provide controlled perimeter exhaustion of the chamber 155. To evacuate the chamber before wafer insertion or removal, a mechanical pump 230 and a turbo pump 240 are provided, both of which communicate with the interior region 111 of chamber 155. Pump 230 provides a quick pump down of the chamber to a reduced pressure of about 10−2 to about 10−4 torr from which the turbo pump 240 can then pump the chamber down to a pressure as low as about 10−6 torr, if desired.
The particular embodiment shown in
While the preferred embodiments of the invention disclosed herein are described in terms of top and bottom orientations, it will be understood by those skilled in the art that such orientations may be reversed without departing from the invention hereof. Further, the chamber and substrate may be oriented to support the substrate vertically or at some angle between horizontal and vertical, although is such case the range of pressures, flow rates and/or temperatures which may be employed in the device be narrowed because of the need to minimize differential gravity or gas buoyancy effects on a non-horizontal substrate. Still further, the substrate and chamber, while preferably concentric and circular, may also be non-concentric and/or polygonal or another curvilinear configuration. Also, the wavelength output(s) from the light source(s) may be provided outside of the UV and IR ranges if effective to activate specific desired photoreactions or heat particular substrates employed in the chamber. Further still, non-wafer substrates, such as flat panel display substrates, may be advantageously conditioned in the chambers of the invention.
This completes the description of the preferred and alternate embodiments of the invention. Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with the details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention, to the full extent indicated by the general meanings of the terms in which the appended claims are expressed.
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|U.S. Classification||118/724, 156/345.5, 257/E21.252, 118/715|
|International Classification||H01L21/306, C23C16/48, C23F1/00|
|Cooperative Classification||C23F1/00, C23F1/12, H01L21/31116, C23G5/00, H01L21/67115, H01L21/02046, C03C15/00, C03C23/0075|
|European Classification||H01L21/67S2H6, C23G5/00, C23F1/00, C03C15/00, C23F1/12, H01L21/02F2B, C03C23/00F, H01L21/311B2B|
|Sep 29, 2009||FPAY||Fee payment|
Year of fee payment: 4
|Nov 22, 2013||REMI||Maintenance fee reminder mailed|
|Apr 11, 2014||LAPS||Lapse for failure to pay maintenance fees|
|Jun 3, 2014||FP||Expired due to failure to pay maintenance fee|
Effective date: 20140411